George Dvorsky

On Star Trek, surgeons can perform complicated operations without so much as cutting into the patient — and soon this could be the case in real life, as well. Researchers at Caltech have developed a new visualization technique, where highly focused light and ultrasound are applied to illuminate the body's interior, allowing them see what's happening behind the skin — and this could potentially introduce less invasive ways of diagnosing and treating conditions like cancerous tumors.

Prior to this breakthrough, deep light could only be focused about one millimeter inside biological tissue. But Caltech's Changhuei Yang, a professor of electrical engineering and bioengineering and a senior author of the study, has come up with a technique that will allow doctors to peer in at about two and a half millimeters — and possibly even a few inches.

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The new breakthrough is an extension of Yang's previous work on the problem, in which he was able to see through a layer of biological tissue by beaming light and recording its scattered, zigzagging patterns. By playing the recording in reverse, he was able to send the light back through to the other side of the tissue, retracing a clean and unscattered path back to the original source.

But Yang wanted to make images of what was inside the tissue — to get a picture of cells or molecules — so he turned his attention to more tightly focused light beams, and interestingly, sound itself.

Piggybacking off the work of Lihong Wang's group at Washington University in St. Louis (WUSTL), Yang's team utilized a technique where light could be focused, using the high-frequency vibrations of ultrasound which doesn't scatter in tissue, and which interacts with light such that it shifts the light's frequency only slightly. The end result of this "acousto-optic" effect was that light which interacted with ultrasound changed into a slightly different color.

When the acousto-optic effect was applied to tissue, it allowed the researchers to pick up on the color variations and record them — thus creating an image of what lies beneath. The device is also highly versatile; researchers can control where they want to focus the light by moving the ultrasound focus.

And because the method allows the researchers to apply as much power as they want, it opens the door to other possibilities, namely subcutaneous treatments. In addition to being able to "tag" cells or molecules with fluorescent dyes, doctors will very likely use the process to treat conditions like cancer.

To do so, doctors would engage in what is called photodynamic therapy. In this procedure, a drug is given to patients that contains a light-sensitive, cancer-killing compound. Cancer cells like to absorb these compounds, and when light is shined upon them, the cells are destroyed. This technique is currently in use with tissue surfaces — but Yang's technique could allow doctors to reach cancer cells deep inside your body. With a few refinements, Yang's team hopes to extend their reach by as much as four inches within a few years.